1. Field of the Invention
This invention relates generally to dynamic speakers of the plane vibrating-plate, multi-point drive type and, more particularly, is directed to apparatus for supporting the driving mechanism for such a dynamic speaker.
2. Description of the Prior Art
In a dynamic speaker of the plane vibrating-plate or diaphragm type which employs a plurality of magnetic circuits driving a substantially square vibrating plate or diaphragm at a plurality, preferably four, attachment points along diagonals of the square plate, it is important for fidelity of reproduction that the rear surface of the vibrating plate be relatively open to the air. Without a substantial degree of openness, the free movement of the vibrating element or diaphragm is interfered with and the frequency of the dynamic speaker is degraded.
The applicants have discovered that the openness at the rear of the vibrating element is preferably at least 60 percent and that any substantial decrease in openness at the rear of the vibrating element deteriorates the frequency responsive characteristics of the loudspeaker.
Flat-plate loudspeakers of the type described require substantial rigidity in the frame structure which supports the plate-like diaphragm and the magnetic driving elements. The requirement for rigidity limits the amount of openness which can be achieved in the existing rear support structures. The difficulty in providing the requisite openness is further complicated by the fact that the plurality of magnetic driving circuits, themselves, occupy a significant portion of the area opposed to the rear of the vibrating plate-like diaphragm.
Dynamic speakers of the type discussed herein are disclosed in U.S. Pat. No. 4,122,314. As disclosed in the referenced patent, four magnetic driving circuits are disposed at the rear of the flat plate diaphragm and are held in place by a die-cast framework having arms parallel to the sides of the speaker. When installed as described in the referenced patent, the magnetic driving circuits couple the reaction forces from driving the diaphragm back into the support structure and, the support structure is thereby subjected to vibratory movement which interferes with reproduction fidelity.